1. Field of the Invention
The present invention relates to a process cartridge and an electrophotographic apparatus, and in particular to an intermediate transfer belt-electrophotographic photosensitive member integrated process cartridge and an electrophotographic apparatus having the process cartridge.
2. Related Background Art
An image forming apparatus of an electrophotographic system (electrophotographic apparatus) using a belt-shaped intermediate transferring member (intermediate transfer belt) is effective as a color electrophotographic apparatus and as a multi-color image forming apparatus which brings a plurality of component color images of color image information or multi-color image information into sequential lamination transfer so as to output image formed matter synthesized and reproduced from color images and multicolor images.
Compared with a conventional color electrophotographic apparatus (for example, Japanese Patent Application Laid-Open No. 63-301960, etc.) of a system in which images are transferred from an electrophotographic photosensitive member to a transfer material fastened or attracted onto a transferring drum, a color electrophotographic apparatus using an intermediate transfer belt does not require any processing or control (for example, prehension to a gripper or absorbing, giving curvature, etc.) on the transfer material but can transfer images from the intermediate transfer belt, and therefore has an advantage that various kinds of transfer material can be selected regardless of wideness/narrowness of the width or the longness/shortness of the length to cover thin paper (40 g/m2 paper) to thick paper (200 g/m2 paper) such as envelopes, postcards, and label forms, etc.
In addition, compared with such a case where an intermediate transfer member (intermediate transfer drum) in a rigid drum shape is used, adopting an intermediate transfer belt shape for the intermediate transfer member, freedom for disposing inside an electrophotographic apparatus increases, giving rise to an advantage that miniaturization or cost reduction of the main body of the electrophotographic apparatus can be implemented by efficiently utilizing spaces.
In addition, as a photoconductive material used for the electrophotographic photosensitive member which the electrophotographic apparatus comprises, inorganic materials such as zinc oxide, selenium and cadmium sulfide, etc. are known.
As compared with inorganic materials, organic materials such as polyvinyl carbazole, phthalocyanine, and azo pigment have advantages such as high production efficiency or pollution-free performance, and in particular are superior in photoconductivity. Organic electrophotographic photosensitive members using such organic materials are widely used for electrophotographic apparatuses.
An intermediate transfer belt repeatedly receives bending stress and contact with or rubbing from various kinds of drive members and transfer members, etc., every time it rotates, and with a high potential being applied, its life is shorter than the main body of an electrophotographic apparatus, and replacement is indispensable under the current state.
Likewise, the electrophotographic photosensitive member is also repeatedly affected by electrification, exposure, development, transfer, cleaning, and dielectrification, and therefore requires various chemical or physical endurance, and thus an organic electrophotographic photosensitive member needs to be replaced as well.
Otherwise, waste toner having collected residual toner on an intermediate transfer belt needs treatment, and a lot of components such as an electrophotographic photosensitive member, developing means and toner, etc. need replacement and maintenance.
As a method to unitize these replacement components and attach to/remove from the main body of an electrophotographic apparatus easily, Japanese Patent Application Laid-Open No. 8-137181 proposes to dispose an intermediate transfer belt and an electrophotographic photosensitive member as respectively independent units detachably mountable to the main body of an electrophotographic apparatus without difficulty.
However, these means involve a number of replacement units to make the user""s operation complicated. Moreover, the intermediate transfer unit and the electrophotographic photosensitive member unit are respectively designed and disposed independently, thereby causing such a problem that the main body of the electrophotographic apparatus becomes larger or costs increase.
As a means to solve this problem, replacing means to cause the intermediate transfer belt and the electrophotographic photosensitive member (replacement parts) to be supported integrally as one body in one unit, and to be constructed so as to cause it to be simultaneously removed from/attached to the main body of the electrophotographic apparatus are suitable, and are proposed in Japanese Patent Application Laid-Open No. 6-110261, Japanese Patent Application Laid-Open No.10-177329, and Japanese Patent Application Laid-Open No. 11-30944.
However, the method to construct the intermediate transfer belt and the electrophotographic photosensitive member as one-body unit to become an intermediate transfer belt-electrophotographic photosensitive member integrated process cartridge that is detachably mountable to the main body of the electrophotographic apparatus gives rise to several problems originated from the intermediate transfer belt.
In particular, what causes a big problem is a characteristic abnormality of the electrophotographic photosensitive member and the intermediate transfer belt that takes place when the intermediate transferring member and the electrophotographic photosensitive member are left to stand for a long time while they are integrally provided under a state of one body.
The electrophotographic photosensitive member as well as the intermediate transfer belt contain various materials being mixed in order to obtain required functions, and among those materials some may affect adversely each other by being left for a long time.
For example, in case when a material permeating into constructing components, such as a binder resin, to make it plastic or a material influencing movement of electric charges, are attached, in particular, an organic electrophotographic photosensitive member is apt to be influenced thereby.
In the case of matter influencing movements of electric charges being attached to the electrophotographic photosensitive member, the difference in sensitivity characteristic is brought about in that portion, giving rise to a density difference from the neighborhood at the time of printing to provide an abnormal image.
Also, as for the intermediate transfer belt, partial changes in electric characteristics such as resistance or capacity will result in transfer unevenness, which will appear in the image.
The most serious problem is the case where a crack occurs in the photosensitive layer due to the matter having migrated from the intermediate transfer belt. Such a crack is remarkable in the thickest layer among the layers constituting the photosensitive layer, and is apt to occur in the photosensitive layer and in the charge transport layer in case of lamination type photosensitive layers.
Such a phenomenon that a crack occurs in the electrophotographic photosensitive member or a shift in matter influencing movements of electric charges takes place remarkably in a portion (contact part) where the intermediate transfer belt and electrophotographic photosensitive member are brought into contact, but in case of the matter in question being volatile, not only the contact part but also the neighborhood is affected so that unevenness in the image density is caused to take place.
Accordingly, even if the intermediate transfer belt and the electrophotographic photosensitive member are not always brought into contact, in case of an intermediate transfer belt-electrophotographic photosensitive member integrated process cartridge which is disposed in the same housing, leaving the integrated process cartridge to stand for a long time could give rise to an abnormal image.
Such a phenomenon has been found out to be accelerated faster in particular in an environment of higher temperature, and also as for moisture, higher moisture tends to give rise to bad effects, and therefore, it is necessary that no problem occurs in the intermediate transfer belt-electrophotographic photosensitive member integrated process cartridge due to temperature and humidity applied during the distribution stage.
On the other hand, in many cases this phenomenon will not be problematic very much after the electrophotographic apparatus has been installed and started to be used.
The reason thereof is as follows: the environment in which an electrophotographic apparatus, such as a photocopier or a printer, is used seldom becomes an environment of high temperature and high humidity the same as those applied during the physical distribution, and moreover, when an image is formed, a part of the toner used and an external additive on the surface of the toner particles, although in a very small quantity, remains between the electrophotographic photosensitive member and the intermediate transfer belt so that mutual material movements between the electrophotographic photosensitive member and the intermediate transfer belt are prevented.
In particular, in recent years, the technology of electrophotographic apparatus has progressed, and for a printer or a photocopier of a digital developing system, enhancement in size reduction or the high density of an exposing spot diameter has enabled delicate pixel development with 600 dpi or more, and in addition thereto, precise control of an electric field, etc., has made a high quality image available.
As a result, a minor abnormality of the electrophotographic photosensitive member and the intermediate transferring member, which has caused no trouble in the conventional techniques, may influence image quality, and a solution of this problem is important.
However, in the above described conventional technology, measures are not taken to cope with such a situation that the intermediate transfer belt-electrophotographic photosensitive member integrated process cartridge left standing for a long time during transportation and storage, and no distribution process is taken into consideration in designing the integrated process cartridge, giving rise to a possibility of damaging the image quality unless the storage management and service period are severely controlled on the process cartridge and bringing about problems such as increased management costs and user frequent complaints.
In addition, reduction of running costs is an important problem, and thus the intermediate transfer belt-electrophotographic photosensitive member integrated process cartridge as a replacement part needs further cost reduction, and therefore in order to make handling easy, attention must be paid to miniaturization as well as treatment of waste toner as well.
As above, those which have solved the problems in the intermediate transfer belt-electrophotographic photosensitive member integrated process cartridge are not yet available.
The object of the present invention is to solve the above described problems and to provide a process cartridge that makes maintenance easy, can attain miniaturization as well as cost reduction of the electrophotographic apparatus which is attached/removed, and can provide good images, and an electrophotographic apparatus having the process cartridge.
The present invention provides a process cartridge which is detachably mountable to a main body of an electrophotographic apparatus, integrally comprising:
an electrophotographic photosensitive member to carry a toner image;
an intermediate transfer belt having a contact part with the electrophotographic photosensitive member, and
primary transfer means to primarily transfer the toner image at the contact part from the electrophotographic photosensitive member to the intermediate transfer belt,
wherein after the contact part is formed by the electrophotographic photosensitive member and the intermediate transfer belt being brought into contact with each other under a linear pressure of 0.5 N/cm and left to stand for 10 hours in an environment of 45xc2x0 C./95% RH, differences in the dark portion potential and the light portion potential of the electrophotographic photosensitive member between the contact part and the portion being not the contact part of the electrophotographic photosensitive member are respectively less than 20%, and no crack having a length of not less than 1 mm occurs in any of the surface of the electrophotographic photosensitive member and the surface of the intermediate transfer belt.
In addition, the present invention provides an electrophotographic apparatus comprising:
an electrophotographic photosensitive member to carry a toner image;
charging means to electrically charge the electrophotographic photosensitive member;
exposing means to form an electrostatic latent image on the electrophotographic photosensitive member charged with the charging means;
developing means to develop with a toner the electrostatic latent image formed with the exposing means on the electrophotographic photosensitive member to form a toner image on the electrophotographic photosensitive member;
an intermediate transfer belt having a contact part with the electrophotographic photosensitive member to perform, after primary transfer of the toner image from the electrophotographic photosensitive member to the intermediate transfer belt, secondary transfer of the primarily transferred toner image to a transfer material; and
primary transfer means to primarily transfer the toner image from the electrophotographic photosensitive member to the intermediate transfer belt at the contact part; and
comprising a process cartridge integrally supporting at least the electrophotographic photosensitive member, the intermediate transfer belt, and the primary transfer means and being freely detachably mountable to the electrophotographic apparatus main body,
wherein after the contact part is formed by the electrophotographic photosensitive member and the intermediate transfer belt being brought into contact with each other under a linear pressure of 0.5 N/cm and left to stand for 10 hours in an environment of 45xc2x0 C./95% RH, differences in the dark portion potential and the light portion potential of the electrophotographic photosensitive member between the contact part and the portion being not the contact part of the electrophotographic photosensitive member are respectively less than 20%, and no crack having a length of not less than 1 mm occurs in any of the surface of the electrophotographic photosensitive member and the surface of the intermediate transfer belt.